Abstract

The life history, population and feeding biology of two species of frogs (R. cancrivora and R. limnocharis) were studied from April 1992 through September
1993 in the rice growing district of Tanjung Karang, Selangor, Malaysia. The
results showed that the breeding periods of the two frogs were correlated with the
irrigation phase of the rice growing seasons and were not correlated with the
rainfall. The frogs were also found to have two breeding peaks annually as opposed
to a single peak for the same species in other localities.
Comparison of the life history aspects of the two species showed that R. cancrivora females produced more, and larger sized, eggs than R. limnocharis females. This then produced a chain effect whereby R. cancrivora larvae developed
faster and metamorphosed at a larger size than those of R. limnocharis, and then
continued to grow at a faster rate, attained a larger size and reached sexual maturity
earlier. These factors most probably contributed to the observed disparity i n
population size between these two frogs wherein R. cancrivora is about six times
more numerous than R. limnocharis.
The fact that adults of these two species differ in size is also the main reason
as to why they can coexist in the same habitat. Different body sizes allow them to
ingest different sized prey items, as was discovered by analysis of their diets, thus
avoiding competition for food. Survivor ships from eggs to metamorphosis for both
species are low but normal for lentic-water breeding amphibians, and they are
deemed sufficient to maintain the population levels if human interference can be
substantially reduced. Fluctuations in the population structure are mainly due to
recruitment, natural mortality and human interference. The most important food
items for both species are insects and about 80% of these insects are pests of rice.
Hence these frogs are considered very important biological control organisms in the
paddy field habitat.